JP2005509357A - Method for link adaptation processing and transmission power control related to applications - Google Patents

Abstract

A method for transferring information over a between a first node and a second node includes the steps of transmitting a frame from the first node to the second node. The frame contains link data enabling a determination of a link mode. Upon receipt of the frame at second node, a determination is made of a link mode using the link data contained in the frame, and data is transmitted from the second node to the first node using the determined link node.

Description

  This application claims priority to US Provisional Application No. 60 / 344,610, filed Nov. 8, 2001, the entire disclosure of which is hereby incorporated by reference.

  The present invention relates to link adaptation processing, and more particularly to a method for adapting a link without transferring link mode information between communicating nodes.

  The IEEE 802.11 wireless LAN (WLAN) standard was established in 1997, and wireless LAN communication between various nodes became possible. The IEEE 802.11 standard has been extended with a new physical layer based on the OFDM (Orthogonal Frequency Division Multiplexing) scheme. In addition, seven different data rates are realized using advanced QAM (Quadrature Amplitude Modulation) and various convolutional code processes. IEEE 802.11b, a similar standard designed for the 2.4 GHz frequency band, has also been standardized, and this standard also provides four different data rates.

  None of these standards or all existing link adaptation algorithms define an exchange mechanism for sending link adaptation control messages. The lack of an exchange mechanism for link adaptation messages has created a limit on the performance of IEEE 802.11. Designers must rely on indirect suggestions as to whether the correct link adaptation has been chosen. These examples include the presence or absence of certain types of receipt notifications. Therefore, there is a need for a method for controlling link adaptation that does not require explicit link mode signaling.

  The present invention seeks to overcome the above and other problems associated with systems and methods for transferring information over a link between a first node and a second node. A frame is transmitted from the first node to the second node. The frame includes link data. The link data is useful for the second node to determine the link mode for future transfers. When the second node receives the frame, the second node performs link mode determination from the second node to the first node using the link data included in the frame. A transmission from the second node to the first node is performed using the determined link mode.

  The accompanying drawings illustrate embodiments of the invention and include descriptions to explain the principles of the invention. Further, the drawings are provided to enhance the understanding of the present invention, and constitute a part of this specification and are incorporated in the specification.

  In particular, reference is made to FIG. 1 of the accompanying drawings. FIG. 1 shows an example of a traditional link adaptation process. Node A transmits a frame at 10 to allow node B to determine the reception quality. Node B uses this information in certain algorithms or processes 15. This algorithm or process 15 selects the optimum link mode for communication from node A to node B. Subsequently, the node B transmits a notification about a recommended link adaptation (link adaptation: LA) mode to the node A. Node A performs a subsequent transmission 25 using the recommended link mode. This procedure is used repeatedly for subsequent communications, which allows it to adapt continuously to changes in the state of the link. This procedure is similar to closed-loop transmission power control and may be integrated into the power control circuit.

  In some wireless systems, one of the nodes may be physically attached to the access network. The access network may make the decision to use a certain link mode. Here, the other nodes may only provide recommendation information about the link mode, or may only send a measurement report. The result is some asymmetry. Although this is not clear from FIG. 1, node A and node B are not equal to each other. The main problem with this type of system is that the detailed signaling method for IEEE 802.11 is not defined. This method is therefore only applicable when the standard can be extended using link adaptive signaling.

  One possible link adaptation scheme for IEEE 802.11 is to use indirect feedback. Of course, this method also lacks a clear link adaptation feedback mechanism. Indirect feedback can be applied by using whether the reception confirmation notification has arrived or has not arrived. The link mode rises or falls as a function of response. However, this approach takes some time to find a suitable rate and forces the communication to endure it. Since frame errors must be deliberately introduced to determine the operating point, the method of increasing / decreasing the rate is not very efficient.

  The problem with traditional link adaptation systems implemented in closed loop systems that need to transmit information between entities is that a signaling scheme for link adaptation is required. Referring to FIG. 2, an open loop link adaptation approach is proposed according to the present invention. This is achieved by taking advantage of the channel reciprocity available in many wireless systems. However, additional information is required to implement this scheme. First, information on transmission power when a frame is transmitted must be provided. The interference level at the receiving node must also be provided (preferably should be suggested in the interference level field). The interference level may be exemplified by a spectrum distribution.

  Reference is made to the method associated with the sequence shown in FIG. 2 and the flowchart shown in FIG. Initially, in step 30, the transmission power level and the interference level of node A are stored in a frame transmitted from node A to node B. In addition, in step 35, several means are included in the frame that allow channel determination. There are two ways to estimate the channel, the so-called pilot sequence (which may be referred to as pilot, pilot symbol, channel estimation sequence / symbol, training sequence / symbol) or the so-called blind channel estimation. is there. Blind channel estimation is not a very common method, but it does not have to rely on a specific pilot sequence. Instead, it uses data carrying symbols (or similar) and certain attributes for the modulation scheme being used. For example, information about the amplitude or phase of an allowed modulation scheme can be used to determine channel information. In the case of a pilot sequence, a receiver holding information about the training sequence can perform good channel estimation. In order to be able to identify the system, the pilot sequence is different between one system and another system, and the pilot sequence is designed to be different between one modulation scheme and another modulation scheme to identify the modulation scheme. For example, a pilot sequence used in IEEE 802.11a is defined in the standard. In step 40, node A transmits a frame to node B, and the frame is received by node B in step S45.

  In the IEEE 802.11 protocol, for example, the frame may be a CF-POLL frame issued from an access point to a station (STA). Node A can transmit the used transmission power and the desired reception power in the same CF-POLL frame. The latter depends on the interference level and reception power level observed at node A.

  In Step 45, if the node B has received the frame from the node A, it is necessary to select a link rate and a link mode for subsequent messages transmitted from the node B to the node A. All of the information is retained. Node B determines the link rate and link mode in step 50. Node B may also take into account past communications and channel information derived in association with (already) when determining the link mode. In the system described with reference to FIG. 1, the node B determines the link mode for transmission from the node A to the node B. In contrast, the transmission from the node B to the node A is performed. Node B may determine the link mode for. Note that the specific algorithm or method used when determining the link rate or link mode using the information loaded in the frame received from the node A can be executed by various methods.

  However, several approaches may be used. One approach would be to apply a radio resource management policy. Radio resource management policies benefit the entire network. Or, apply a policy that a single node tries to make the best use of its own performance without disrupting other communications or harming the interference that occurs. May be. The policy in the IEEE 802.11 network is more similar to the latter, ie, each node tries to maximize its performance. In light of this, each node may attempt to select transmission power as well as link mode. In such a case, a technique that maximizes the throughput of the node is used. Optionally, when using the fastest link mode while maximizing throughput, each node can choose not to transmit using excess power to conserve transmit power and When using the battery life can be extended.

Typical link mode selection methods incorporated as a feature of the present invention include minimizing Node B transmit power under conditions that maximize throughput (and for any fastest rate mode close to the fastest rate). There is a way to do it. This can be conceptualized by the objective function f _q. f _q = f (S _LM , P _TX , H, I), where S _LM represents all link mode combinations, and P _TX is the transmission power allowed for Node B Where H is the determined channel from node A to B (assuming here a reciprocal channel, or at least close to each other), I Represents the interference level at node A. The objective function may be, for example, an expected throughput, but may be another optimization principle (for example, a packet error rate). Here, Q _min which is a certain minimum quality situation is imposed on the objective function f _q as a condition to be _satisfied . Next, the link modes within the set of S _LM is tested in a range that can be taken of the P _TX. A combination that satisfies the situation Q _min and consumes the minimum power P _TX is selected. As an alternative, if P _TX cannot be changed, the link mode that gives the optimum quality with f _q is selected.

  Link adaptation is generally not limited to changing link modes (single coordinate placement and forward error correction coding), it is important that transmit power control may be included. That is, the provided transmission power does not have to be a fixed level. However, according to the original IEEE 802.11 standard, the transmission power is fixed, so link adaptation will only include changes to the link mode (coordinate placement and FEC). Transmission from Node B to Node A is performed at step 55 using the determined link mode.

  Reference is now made to FIGS. These show an extension of the open-loop link adaptation method proposed to achieve closed-loop link adaptation. In the first part of this process, the transmission power level and interference level at node A are stored in the frame at step 60 as described with respect to FIG. The frame is transmitted from the node A to the node B.

  In addition, some means of enabling channel determination is included in the frame at step 65. There are essentially two ways to estimate the channel, the so-called pilot sequence or through the aforementioned blind channel estimation. In step 70, the node A transmits a frame from the node A to the node B, and in step 75, the frame is received. In step 75, when Node B receives the frame from Node A, Node B requires the necessary information to select the link rate / mode for subsequent messages sent from Node B to Node A. Will hold all. Using this information, the Node B determines the link rate / mode in step 80. Transmission from node B to node A is performed at step 85 using the determined link mode.

  When the transmission signal from node B is received at node A using the determined link mode, at step 90, node A uses the optimum link mode when transmitting from node B to node A. Determine whether or not. If the optimal link mode is used, control returns to step 60 where the transmit power level and interference level information is stored in the frame returned to the Node B. On the other hand, when it is determined that the optimum link mode has not been used, the node A performs the link mode change for the subsequent transmission from the node B. That is, in step 95, change the link mode by manipulating the indicated transmit power level, interference level, or both, and storing the altered version in the frame returned to the Node B. Is executed. Non-optimal link modes can lead to improper setting of power levels or inaccurate measurements present in the channel transmission signal. This will continue until the optimal link mode is reached.

  If other stations (stations) that accidentally receive communications misunderstand the link rate margin of whether or not to adjust as described above, a specific situation will arise. For example, in Node A, the interference level (or transmission power level if possible) suggested by the expansion of the closed loop may later lead to a problem situation where incorrect link adaptation or transmission power is used. There is a fear. It is not clear whether this is a significant problem. However, to avoid this, we propose two methods that require normalization. These implementations are optional.

  The first way is to be able to transmit only the first frame in the frame exchange sequence. Examples of such frames are RTS, CTS and CF-POLL in IEEE 802.11. Since performing any closed-loop adaptation on the first two frames makes little sense, these frames should be adjusted and should never include the suggested interference level. Therefore, whenever a communication is being received, other stations will be able to determine the correct transmission parameters. It should be standardized as to which frame is used to signal an indication of the correct interference level (or transmission power level if possible).

  The second method is based on adding a bit to the PLCP (Physical Layer Convergence Protocol) service field to identify whether the correct parameters are indicated. One use of this bit is to signal whether closed loop mode or open loop mode is being used. In an open loop, other STAs may use unrestricted information without restriction, and if signaled that they are closed loop, other STAs will be aware of that information. Should be used. It would be effective to signal that it is open loop for the first two frames.

  A further advantage for closed-loop expansion may be that it can be useful when the links are not reciprocal, such as when various antenna diversity configurations are employed. Closed loop expansion is also directly applicable in extending open loop power control to closed loop power control. This is because link adaptation and power control are complementarily operated in different signal-to-noise ratio regions.

  Although the present invention has been described in the context of IEEE 802.11, those skilled in the art will clearly understand that the present invention is applicable in other standards, systems and others with similar conditions. Like.

The “interference field” and “transmit power field” may similarly relate to vector quantities rather than just scalar quantities. The reason for this is not only the various signal coordinate arrangements (or any more general modulation scheme) and forward error correction over a single radio channel, but also the transmitter, receiver or both have multiple antennas. This is because the link mode may include multiple parallel radio channels that are always used when used, and associated code processing and modulation processing. When N transmit antennas and M receive antennas are employed, in effect M * N channels can be used. This is referred to as a multiple input multiple output (MIMO) channel, and forward error correction codes can be used to increase robustness, spectral efficiency, or both.

  As an alternative, the transmitter has N antennas and the receiver has only one antenna. This type of channel is called MISO (Multiple Input Single Output) and is mainly used to increase the robustness of communication. Although a SIMO (single input multiple output) channel exists as a concept, there is no need to use a vector quantity suggestion on the transmission side. This is because the transmitter has only one antenna. Various types of forward error correction coding methods have been developed and are under development. This is a relatively new field of research on MIMO and MISO communications, and these have only begun in the last few years. In the current classification, since the classification is still missing for the encoding of MIMO / MISO, various names are overflowing in the research field. Examples of codes that can be used in a MIMO / MISO channel include STC (Space Time Coding), MIMO code (available only for MIMO), transmit diversity (available only for MISO), MISO code ( And BLAST (Bell Labs Layered Space-Time: Bell Labs, Multi-layered Space-Time) code (available only for MIMO).

  The operation and structure of the present invention will be apparent from the above description. Although the invention has been characterized, illustrated and described as specific embodiments, changes and modifications can be made without departing from the invention as defined in the appended claims.

FIG. 1 is a diagram illustrating a traditional link adaptation process. FIG. 2 is a diagram showing a link adaptation process according to the method of the present invention. FIG. 3 is a flowchart illustrating the method associated with FIG. FIG. 4 illustrates the method of the present invention in a closed loop. FIG. 5 is a block diagram for explaining the method shown in FIG.

Claims (26)

A method for transferring information via a link between a first node and a second node, comprising:
(A) transferring a frame carrying link data from the first node to the second node;
(B) receiving the frame at the second node;
(C) determining a link mode from the first node to the second node using the link data at the second node;
(D) transmitting data from the first node to the second node using the determined link mode.   The method of claim 1, wherein the link data includes means for determining a transmit power level, an interference level, and a channel.   The method of claim 1, wherein the link data further includes a pilot sequence.   The method of claim 2, further comprising storing the transmission power level and the interference level in the frame prior to transmission to the second node.   The method of claim 2, wherein the interference level includes a spectrum distribution.   The method of claim 1, further comprising repeating the steps (a)-(d) when transmitting subsequent frames.   The method of claim 1, further comprising: determining transmission power using the link data. Receiving the data transmitted from the second node at the first node;
Determining whether an optimal link mode has been used for the data transmitted from the second node to the first node;
If the optimal link mode is not used, the method further comprises the step of transmitting a second frame carrying the adjusted link data from the first node to the second node. The method of claim 1.   9. The method of claim 8, further comprising determining a new link mode using the adjusted link data at the second node.   The method of claim 8, wherein the adjusted link data is selected to achieve a substantially optimal link mode.   The method according to claim 1, wherein the link data includes a vector quantity. A method for transferring information via a link between a first node and a second node, comprising:
(A) transferring a frame carrying link data including means for determining a transmission power level, an interference level and a channel from the first node to the second node;
(B) receiving the frame at the second node;
(C) determining a link mode from the first node to the second node using the link data at the second node;
(D) transmitting data from the first node to the second node using the determined link mode;
(E) receiving the data transmitted from the first node to the second node;
(F) determining whether an optimal link mode has been used for the data transmitted from the second node to the first node;
(G) If the optimal link mode is not used, the adjusted link data selected to achieve a substantially optimal link mode from the first node to the second node. Transmitting the mounted second frame.   The method of claim 12, further comprising storing the transmit power level and the interference level in the frame prior to transmission to the second node.   13. The method of claim 12, further comprising repeating the steps (a)-(g) when transmitting subsequent frames.   The method of claim 12, further comprising determining transmit power using the link data.   The method of claim 12, wherein the interference level includes a spectrum distribution.   The method of claim 12, further comprising: determining a new link mode using the adjusted link data at the second node. A communication system including a first node and a second node,
The first node is configured to transmit a frame carrying link data from the first node to the second node;
The second node receives the frame at the second node and uses the link data to determine a link mode from the second node to the first node. A communication system configured to transmit data from the second node to the first node using the link mode.   The communication system of claim 18, wherein the link data includes means for determining a transmit power level, an interference level, and a channel.   The communication system according to claim 19, wherein the first node further stores the transmission power level and the interference level in the frame prior to transmission to the second node.   The communication system according to claim 19, wherein the interference level includes a spectrum distribution.   The communication according to claim 18, wherein the first node repeatedly executes the reception, the determination, and the transmission when transmitting a subsequent frame from the first node. system.   The communication system according to claim 18, wherein the second node uses the link data to determine transmission power.   The first node receives the data transmitted from the second node at the first node, and is optimal for the data transmitted from the second node to the first node. It is determined whether the link mode is used. If the optimum link mode is not used, a second frame carrying the adjusted link data is transmitted from the first node to the second node. The communication system according to claim 18.   The communication system according to claim 24, wherein the second node determines a new link mode by using the adjusted link data in the second node.   The communication system according to claim 24, wherein the adjusted link data is selected so as to achieve a substantially optimal link mode.

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